Power semiconductor devices, also known as power devices, are known in the art and used as switches or rectifiers in power electronic circuits. In wind turbines, power semiconductor devices can be used to connect the generator with the grid. In some wind turbines power converters (comprising semiconductor devices) controls the power flow to the grid.
Power devices comprises, at least one semiconductor chip, (also known as a chip) conventionally made from silicon, but can also be made of silicon carbide or any other suitable material. When exerting a power device to a current, the chip will heat due to the internal losses in the chip. This can lead to degeneration of the chip, bondwire liftoffs or any other degeneration or wearout of the power device.
It is known in the art that the temperature of a chip is related to the current and/or the voltage in a power device. In EP 1 983 640 it is disclosed that there is a close connection between the voltage drop over the power device and the temperature.
In DE10351843A1 it is disclosed to determine the temperature of a power semiconductor in an inverter by switching a load current off and on and determining its value. If this lies within a given region the voltage drop at the semiconductor is determined and from this the temperature of the power semiconductor.
The temperature is important for the performance, reliability and end of life time of a chip accommodated in a power device. The temperature should be understood, as both changes in the temperature and the mean value.